Once a RestClient instance has been created, a Sniffer can be associated to it. The Sniffer will make use of the provided RestClient to periodically (every 5 minutes by default) fetch the list of current nodes from the cluster and update them by calling RestClient#setHosts.

Sniffer sniffer = Sniffer.builder(restClient).build();

It is important to close the Sniffer so that its background thread gets properly shutdown and all of its resources are released. The Sniffer object should have the same lifecycle as the RestClient and get closed right before the client:


The Elasticsearch Nodes Info api doesn’t return the protocol to use when connecting to the nodes but only their host:port key-pair, hence http is used by default. In case https should be used instead, the ElasticsearchHostsSniffer object has to be manually created and provided as follows:

HostsSniffer hostsSniffer = new ElasticsearchHostsSniffer(restClient,
Sniffer sniffer = Sniffer.builder(restClient)

In the same way it is also possible to customize the sniffRequestTimeout, which defaults to one second. That is the timeout parameter provided as a querystring parameter when calling the Nodes Info api, so that when the timeout expires on the server side, a valid response is still returned although it may contain only a subset of the nodes that are part of the cluster, the ones that have responsed until then. Also, a custom HostsSniffer implementation can be provided for advanced use-cases that may require fetching the hosts from external sources.

The Sniffer updates the nodes by default every 5 minutes. This interval can be customized by providing it (in milliseconds) as follows:

Sniffer sniffer = Sniffer.builder(restClient)

It is also possible to enable sniffing on failure, meaning that after each failure the nodes list gets updated straightaway rather than at the following ordinary sniffing round. In this case a SniffOnFailureListener needs to be created at first and provided at RestClient creation. Also once the Sniffer is later created, it needs to be associated with that same SniffOnFailureListener instance, which will be notified at each failure and use the Sniffer to perform the additional sniffing round as described.

SniffOnFailureListener sniffOnFailureListener = new SniffOnFailureListener();
RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200))
Sniffer sniffer = Sniffer.builder(restClient).build();

When using sniffing on failure, not only do the nodes get updated after each failure, but an additional sniffing round is also scheduled sooner than usual, by default one minute after the failure, assuming that things will go back to normal and we want to detect that as soon as possible. Said interval can be customized at Sniffer creation time as follows:

Sniffer sniffer = Sniffer.builder(restClient)

Note that this last configuration parameter has no effect in case sniffing on failure is not enabled like explained above.